It has been suggested that hyperlipidemia may contribute to the progression of renal disease via the deleterious effects of oxidized low-density lipoprotein (LDL) on the glomerular mesangium. Because estrogens possess potent antioxidant activity, we sought to determine whether sex hormones influence the oxidation of LDL by mesangial cells. Rat mesangial cells were incubated with LDL (200 micrograms/ml), and the extent of lipid oxidation was assessed by the generation of thiobarbituric acid reactive substances (TBARS), by increased electrophoretic mobility, and by enhanced uptake of mesangial cell-modified LDL by macrophages. A progressive rise in TBARS and an increase in electrophoretic mobility was observed on incubation of LDL with mesangial cells. Coincubation with estradiol (10 mumol/L) reduced TBARS generation by 46% at 36 hours (p < 0.01) and reversed the increase in relative electrophoretic mobility (1.25 +/- 0.07 vs 1.01 +/- 0.03, p < 0.05). LDL that had been oxidized by mesangial cells in the presence of estradiol (10 mumol/L) showed reduced uptake by macrophages when compared with LDL that had been oxidized by mesangial cells in the absence of estradiol (14 +/- 2 pmol/10(6) cells per hour vs 22 +/- 3 pmol/10(6) cells per hour, p < 0.05). In contrast, neither testosterone nor estrone had any effect on these parameters. We conclude that estradiol, by virtue of its antioxidant properties, inhibits mesangial cell-mediated oxidation of LDL and reduces the uptake of mesangial cell-modified LDL by macrophages.